The present invention relates to a liquid crystal display device and, more particularly, to a liquid crystal display device of the In-Plane Switching Mode type.
A liquid crystal display device of the In-Plane Switching Mode type has a construction in which a pixel electrode and a counter electrode are formed in each liquid-crystal-side pixel area of one of two substrates disposed in opposition to each other with a liquid crystal material interposed therebetween, so that the optical transmissivity of the liquid crystal material is controlled by a component approximately parallel to the substrates, which component is contained in an electric field generated between the pixel electrode and the counter electrode.
One known type of such a liquid crystal display device has a construction in which a pixel electrode and a counter electrode are respectively formed in different layers with an insulating film interposed therebetween and either one of the pixel and counter electrodes is formed as a transparent electrode approximately over the whole of each pixel area, while the other is formed as a plurality of stripe-shaped transparent electrodes which are disposed approximately over the whole of each pixel area in such a manner as to extend in one direction and to be juxtaposed in a direction transverse to the one direction.
Such a device is described in detail in, for example, K. Tarumi, M. Bremer, and B. Schuler, IEICE TRANS. ELECTRON., VOL. E79-C No. 8, pp. 1035-1039, AUGUST 1996.
Incidentally, a so-called active matrix system is applied to such a liquid crystal display device; for example, each of its pixel areas is surrounded by a pair of adjacent gate signal lines disposed so as to extend in the x direction and to be juxtaposed in the y direction and by a pair of adjacent drain signal lines disposed so as to extend in the y direction and to be juxtaposed in the x direction. Each of the pixel areas is provided with a switching element driven by the supply of a scanning signal from one of the adjacent gate signal lines, and a video signal is supplied to a pixel electrode of the pixel area from one of the adjacent drain signal lines via this switching element.
However, it has been pointed out that a liquid crystal display device constructed in the above-described manner easily suffers from image retention due to an electric field approximately perpendicular to the substrates, which is contained in the electric field generated between the pixel electrode and the counter electrode. In addition, a further improvement in the aperture ratio of the liquid crystal display device has been desired.
The present invention has been made in view of the above-described problem, and provides a liquid crystal display device in which image retention does not easily occur.
The invention also provides a liquid crystal display device in which the aperture ratio is improved.
Representative aspects of the invention disclosed in the present application will be described below in brief.
A liquid crystal display device according to the present invention includes, for example, in each pixel area on a liquid-crystal-side surface of one of substrates disposed in opposition to each other with a liquid crystal interposed therebetween, a thin film transistor to be driven by supply of a scanning signal from a gate signal line, a pixel electrode to be supplied with a video signal from a drain signal line via the thin film transistor, and a counter electrode which causes an electric field to be generated between the counter electrode and the pixel electrode. The counter electrode is formed in a layer overlying the pixel electrode with a stacked insulating film interposed between the counter electrode and the pixel electrode. The stacked insulating film is made of a stacked structure in which an insulating film including a part of a gate insulating film of the thin film transistor, an inorganic material layer and an organic material layer are stacked in that order. The counter electrode is made of a plurality of stripe-shaped counter electrodes which are disposed so as to extend in one direction and to be juxtaposed in a direction transverse to the one direction, and the pixel electrode is made of a transparent plane-shaped electrode which is formed in a large part of the pixel area.
In the liquid crystal display device constructed in this manner the insulating film interposed between the pixel electrode and the counter electrode has a stacked structure in which the inorganic material layer and the organic material layer are stacked in that order, whereby the dielectric constant of the insulating film can be made small and the thickness thereof can easily be made large. Accordingly image retention due to an electric field occurring in a direction approximately perpendicular to the substrates does not easily occur.
In the construction of the liquid crystal display device according to the invention, the plurality of counter electrodes are formed to extend approximately in parallel with the drain signal line and include a counter electrode which is superposed on the drain signal line and which has a central axis approximately coincident with a central axis of the drain signal line and is wider than the drain signal line.
In the liquid crystal display device constructed in this manner, since the counter electrode is formed so as to be superposed on an area in which the drain signal line is formed, an improvement in aperture ratio can be realized.